PDP apparatuses have relative ease in increasing a screen size, when compared with CRT display apparatuses which are currently most common image display apparatuses. Therefore, PDP apparatuses attract attention as image display apparatuses suitable for high-definition broadcasting. Here, PDP apparatuses can be classified into alternating current (AC) and direct current (DC) types. At present, AC-type PDP apparatuses form a mainstream because of their superiority in a variety of aspects such as reliability and display quality. (Hereinafter, the term PDP apparatus refers to AC types.)
A PDP apparatus is constituted by a panel unit and a driving unit. The panel unit includes a front panel in which a plurality of pairs of a scan electrode and a sustain electrode are provided, and a back panel on which a plurality of data electrodes are provided. The front panel and the back panel are arranged so as to oppose each other with a space therebetween. Here, the front panel and the back panel are aligned so that the data electrodes intersect the scan electrodes and the sustain electrodes. The front panel and the back panel are sealed together at their peripheral portions. Furthermore, a rare gas such as Ne, Xe and He is enclosed in the space (a discharge space) between the front and back panels. In this way, discharge cells are formed at areas where the data electrodes intersect the scan and sustain electrodes.
This PDP apparatus is generally driven using a field timesharing gradation display method. According to this method, one field (one frame) is divided into a plurality of sub-fields each of which includes a write period and a sustain period. In this way, a duration of lighting is time-divided. Furthermore, images of the sub-fields are combined, to express a gray-scale image for the field.
Regarding such PDP apparatuses, there is a demand for a larger screen and higher definition. To meet this demand, it is required to further reduce degradation in display quality due to electric resistances of scan electrodes and sustain electrodes on a front panel. In detail, since the scan electrodes and the sustain electrodes are usually disposed so as to extend in a lengthwise direction of the front panel, an increase in size of the front panel particularly tends to cause an increase in resistance of the scan and sustain electrodes. Consequently, when electric currents are supplied to the scan and sustain electrodes to drive a PDP apparatus, a significant voltage drop occurs, and the display quality is degraded. This is particularly noticeable in a sustain period. In the sustain period, a discharge current E0 flows in each discharge cell in a very short time period of approximately several hundred nanoseconds from a start of a discharge, as shown in FIG. 11. The sum of the amounts of discharge currents E0 flowing in all of the discharge cells formed by the individual scan and sustain electrodes is equal to the amount of a current Et0 flowing in the individual scan and sustain electrodes, as shown in FIG. 12. As a result, a noticeable voltage drop occurs in the scan and sustain electrodes. This results in lower display quality of the PDP apparatus.
To prevent such a voltage drop of scan and sustain electrodes in a sustain period, it has been considered and attempted to differentiate discharge cells in terms of discharge start timing. For example, Japanese patent application publication No. H11-149274 discloses a driving method in which a pulse is applied to data electrodes forming selected discharge cells in a sustain period. This pulse rises before pulses are applied to scan and sustain electrodes, and falls immediately after a discharge caused by the pulses applied to the scan and sustain electrodes is completed. According to this technique, a discharge starts at a different timing between in the selected discharge cells and remaining not-selected discharge cells. This prevents a large current from flowing into the scan and sustain electrodes in a short time, thereby reducing occurrence of a voltage drop.
In addition, Japanese patent application publication No. H10-133622 discloses the following driving method. In a sustain period, each data electrode is set to a different potential, or data electrodes are grouped so that each group of data electrodes is set at a different potential. According to this technique, a discharge starts at a different timing among discharge cells, or discharge cell groups corresponding to the data electrode groups. This lowers a peak value of discharge currents flowing into scan and sustain electrodes in the sustain period.
As described above, driving of a PDP apparatus is controlled, by means of two options of whether or not to apply the pulse to the data electrodes (Japanese patent application publication No. H11-149264), or by means of two options of whether to apply a pulse of high or low potential (Japanese patent application publication No. H10-133622). According to these techniques, discharge currents in the scan and sustain electrodes are divided into only two groups. Therefore, only little effect is achieved by differentiating discharge currents. The effect can possibly be improved by increasing the number of potential levels for pulses applied to data electrodes, based on the technical idea disclosed in the latter patent application publication. However, an increase in number of potential levels causes an increase in number of necessary power sources. This increase leads to a higher manufacturing cost of a driving unit and unevenness of luminance among discharge cells. For this reason, this alternative method is hardly realistic.